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Cold Cavity BPM R&D for the ILC. Manfred Wendt Fermilab. The International Linear Collider. ILC Beam Parameters (nominal):. ILC Beam Instrumentation. ~ 2000 Button/stripline BPM’s ~ 1800 Cavity BPM’s (warm) 770 Cavity BPM’s (cold, part of the cryostat) 21 LASER Wirescanners - PowerPoint PPT Presentation
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November 30, 2006 CARE Workshop Global Design Effort 1
Cold Cavity BPM R&Dfor the ILC
Manfred Wendt
Fermilab
November 30, 2006 CARE Workshop Global Design Effort 2
The International Linear Collider
beam energy = 2 x 250 GeV
luminosity L = 2 x 1034
rep. frequency frep = 5 Hz
macro pulse length tpulse = 800 µs
# of bunches per pulse = 2820
bunch spacing Δtb = 308 ns
bunch charge = 3.2 nC
bunch length σz ≈ 300 µm
vert. emittance γ εy* = 0.04 mm mrad
RMS energy spread = 0.1 %
βx* (IP) = 21 mm
βy* (IP) = 0.4 mm
hor. beamsize (IP) σx = 500 nm
vert. beamsize (IP) σy = 5 nm
ILC Beam Parameters (nominal):
November 30, 2006 CARE Workshop Global Design Effort 3
ILC Beam Instrumentation
• ~ 2000 Button/stripline BPM’s• ~ 1800 Cavity BPM’s (warm)• 770 Cavity BPM’s (cold, part of the cryostat)• 21 LASER Wirescanners• 20 Wirescanners (traditional)• 15 Deflecting Mode Cavities (bunchlenght)• ~ 1600 BLM’s• Many other beam monitors, including toroids, beam
phase monitors, wall current monitors, faraday cups, OTR & other screen monitors, sync light monitors, streak cameras, feedback systems, etc.
November 30, 2006 CARE Workshop Global Design Effort 4
Cold BPM Requirements• BPM location in the cryostat, at the SC-quad• Every 3rd cryostat is equipped with a BPM/quad:
650x cold BPM’s total.– Real estate: ~ 170 mm length, 78 mm beam pipe
diameter (???).– Cryogenic environment (~ 4 K)– Cleanroom class 100 certification (SC-cavities nearby!)– UHV certification
• < 1 µm single bunch resolution, i.e. measurement (integration) time < 300 ns.
• < 200 µm error between electrical BPM center and magnetic center of the quad.
• Related issues:– RF signal feedthroughs.– Cabling in the cryostat– Read-out System
November 30, 2006 CARE Workshop Global Design Effort 5
Possible Cold BPM Solutions
• Dedicated, high resolution BPM (baseline design):
Cavity BPM, based on the characterization of beam excited dipole eigenmodes, also requires the measurement of the monopole modes for normalization and evt. sign of the beam displacement.
• Combination of dedicated, lower resolution BPM’s and HOM coupler signal BPM’s (alternative design):– Simple, button style BPM’s (~ 50 µm resolution) for
machine tune-up and single bunch orbit measurements.– HOM coupler BPM signal processor as high resolution
BPM
November 30, 2006 CARE Workshop Global Design Effort 6
Cavity BPM PrincipleProblems with simple“Pill-Box” Cavity BPM’s• TM010 monopole
common mode (CM)• Cross-talk (xy-axes,
polarization)• Transient response
(single-bunch measurements)
• Wake-potential (heat-load, BBU)
• Cryogenic and cleanroom requirements
November 30, 2006 CARE Workshop Global Design Effort 7
CM-free Cavity BPM• uses waveguide ports to
suppress the monopole mode (no hybrid-junction required)
+ very high resolution potential (~ 20 nm)!
– complicated mechanics, i.e. cleanroom and cryogenic issues
November 30, 2006 CARE Workshop Global Design Effort 8
KEK ATF nanoBPM CollaborationBINP cavity BPM:• C-Band (6426 MHz)• 20 mm aperture• Selective dipole-
mode waveguide couplers
• 3 BPM’s in a LLBL hexapod spaceframe (6 degrees of freedom for alignment)
• Dual-downconversion electronics (476 & 25 MHz)
• 14-bit, 100 MSPS digitizer
November 30, 2006 CARE Workshop Global Design Effort 9
November 30, 2006 CARE Workshop Global Design Effort 10
Cavity BPM Resolution at ATF• 10 minute run• 800 samples• σ ≈ 24 nm
Move BPM in 1 µm steps
November 30, 2006 CARE Workshop Global Design Effort 11
SLAC Cavity BPM
+ S-Band design for 35 mm beam-pipe aperture
+ Waveguide cut to beam-pipe (better cleaning)
+ Successful beam measurements at SLAC-ESA (~ 0.8 µm resolution)
– No cryogenic temperature tests so far.
– No clean-room certification– Needs a reference cavity or
signal– Reduced beam-pipe
aperture (nominal: 78 mm)
November 30, 2006 CARE Workshop Global Design Effort 12
November 30, 2006 CARE Workshop Global Design Effort 13
November 30, 2006 CARE Workshop Global Design Effort 14
November 30, 2006 CARE Workshop Global Design Effort 15
November 30, 2006 CARE Workshop Global Design Effort 16
Cold L-Band Cavity BPM Design• Waveguide-loaded pillbox with slot coupling.• Dimensioning for f010 and f110 symmetric to fRF,
fRF = 1.3 GHz, f010 ≈ 1.1 GHz, f110 ≈ 1.5 GHz.• Dipole- and monopole ports, no reference cavity for
intensity signal normalization and signal phase (sign).• Qload ≈ 600 (~ 10 % cross-talk at 300 ns bunch-to-
bunch spacing).• Minimization of the X-Y cross-talk (dimple tuning).• Simple (cleanable) mechanics.• Iteration of EM-simulations for optimizing all
dimensions.• Vacuum/cryo tests of the ceramic slot window.• Copper model for bench measurements.
November 30, 2006 CARE Workshop Global Design Effort 17
Scaling of the SLAC Cavity BPM
General viewPorts
Discrete port (current) x=10 mmy=30 mm
Excitation signal
November 30, 2006 CARE Workshop Global Design Effort 18
SLAC BPM (scaled): Eigen Modes
Mode Frequency
1 1.017 – Parasitic E11-like 2 1.023 – Parasitic E21-like3 1.121 – Monopole E01 4 1.198 - Waveguide5 1.465 - Dipole E11
6 1.627
Dipole
Parasitic mode. Coupling throughhorizontal slots is clearly seen
Parasitic modeEz distribution
November 30, 2006 CARE Workshop Global Design Effort 19
Pillbox with WG Slot Coupling
November 30, 2006 CARE Workshop Global Design Effort 20
Optimization of the Slot Dimensions
• EM: Eigen-mode solver• FD: Frequency-domain solver• Slot-L = 55 mm & Slot-W = 5 mm Qload = 678
Q external and Q loaded vs slot length
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
30 40 50 60 70 80
Slot length, mm
Q
Q ext EM
Q load EM
Q load FD
Qload (EM) vs Slot_W (Slot_L=55)
0
200
400
600
800
1000
1200
1400
1 2 3 4 5 6 7 8 9
Width, mm
Q
November 30, 2006 CARE Workshop Global Design Effort 21
Ceramic Windows in the Coupling Slots
Frequency, GHz 1.46
Loaded Q ~ 600
Beam pipe radius, mm 39
Cell radius, mm 114
Cell gap, mm 10
Waveguide, mm 122x110x25
Coupling slot, mm 47x5x3
Window –Ceramic brick of alumina 96%
r ≈ 9.4
Size: the same as slot
N type receptacle,50 Ohm,D=9.75 mmd=3.05 mm
November 30, 2006 CARE Workshop Global Design Effort 22
Matched WG-to-Coaxial Transition
47.03.mm
2
1
Diam. 4.46 mm
11.13 mm 8.9 mm
November 30, 2006 CARE Workshop Global Design Effort 23
Dipole Mode Sensitivity (Resolution)
x
q
Q
R
QQZfxxV
x
sh
11000110110
11)(
GHzxf 46.1)(110 500Z
600Q
141
110
mmx
sh
Q
R
20000 Q
nCq 1
with:
nCVxxV /10145.4)( 3110
mnCmVV /4110 VBWTkZV seThermalNoi 7.00
500Z
KJk /1038.1 23
KT 300
MHzQ
fBW 4.2
110
110
with:
November 30, 2006 CARE Workshop Global Design Effort 24
Monopole-Mode Investigation
Monopole mode damping using simple pin-antennas
November 30, 2006 CARE Workshop Global Design Effort 25
Unmatched Transmission-line Combiner
In-phase signal combining for the monopole-mode signal
• 180 degrees for dipole-mode. Standing wave with some frequency detuning.
• lTL~ 200 mm to avoid resonances around 1.46 GHz (SW eigenmodes for lTL~ 200 mm at: f3 ~1.1 GHz, f5 ~1.9 GHz)
November 30, 2006 CARE Workshop Global Design Effort 26
Combiner-induced Frequency-shift
BPM spectrum vs length of combiner (one leg)
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300 350
mm
GH
z
Quadrupole
Dipole
Monopole
Appropriate length of combiner – reasonable length and non-resonantInteraction with dipole mode
November 30, 2006 CARE Workshop Global Design Effort 27
Test Model for N2 Temperature Cycles
November 30, 2006 CARE Workshop Global Design Effort 28
November 30, 2006 CARE Workshop Global Design Effort 29
November 30, 2006 CARE Workshop Global Design Effort 30
November 30, 2006 CARE Workshop Global Design Effort 31
November 30, 2006 CARE Workshop Global Design Effort 32
L-Band Cavity Assembly
November 30, 2006 CARE Workshop Global Design Effort 33
Next Steps…
• N2 temperature cycles with the test model.
• Drafting of the complete assembly.• EM modeling and fine tuning of the
dimensions.• Investigation of the tolerances.• Prototype manufacturing.• RF measurements and characterization.
Thanks for your patience!